Circuit Description
The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the PCM to calculate the short and long term fuel trim (fuel delivery adjustments). If the oxygen sensors indicate a lean condition, the fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments in order to maintain Air/Fuel Ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition. If the PCM detects an excessively rich condition, diagnostic trouble code (DTC) P0172 sets.
Conditions for Running the DTC
| • | DTCs P0101-P0103, P0107, P0108, P0121-P0123, P0130-P0135, P0137, P0138, P0140, P0141, P0201-P0206, P0300, P0401 , P0403-P0405, P0410, P0412, P0418, P0440, P0442, P0446, P0506, P0507, P1404, or P1441 are not set. |
| • | The engine coolant temperature (ECT) is between 20-110°C (68-239°F). |
| • | The intake air temperature (IAT) is between 18-70°C (64-158°F). |
| • | The manifold absolute pressure (MAP) is between 15-105 kPa (2.1-15.2 psi). |
| • | The vehicle speed is less than 132 km/h (82 mph). |
| • | The engine speed is between 550-4,000 RPM. |
| • | The barometric pressure is more than 70 kPa (10.1 psi). |
| • | The mass air flow (MAF) is between 2.8-150 g/s. |
| • | The fuel level is more than 10 percent. |
Conditions for Setting the DTC
| • | The average long term fuel trim value is below -13 percent. |
| • | All of the above conditions are present for 40 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Fuel contamination, such as water and alcohol will effect the fuel trim. |
| • | A malfunctioning mass air flow (MAF) sensor can cause a rich condition and set this DTC. Refer to DTC P0101 . |
| • | Use a scan tool in order to review the Failure Records. If an intermittent condition is suspected , refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the conditions were not corrected, refer to Fuel System Diagnosis for a possible fuel condition.
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An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a leaking regulator. If the conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
2 |
Important: If any DTCs are set, other than P0172, refer to those DTCs before continuing.
Does the scan tool indicate that the Long Term Fuel Trim is less than the specified value? | -13% | Go to Step 3 | Go to Diagnostic Aids | ||||||||||||
3 |
Does the scan tool indicate that the values are within the specified range and fluctuating? | 200-800 mv | Go to Step 4 | Go to Step 5 | ||||||||||||
4 |
Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 | ||||||||||||
Turn OFF the engine
Did you find and correct the condition? | -- | Go to Step 7 | Go to Fuel System Diagnosis | |||||||||||||
Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 7 | Go to Symptoms - Engine Mechanical in Engine Mechanical | |||||||||||||
7 |
Important: After any of the above repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 8 | ||||||||||||
8 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
